When a traditional battery is discharged, the anode supplies positive ions to an electrolyte and electrons to an external circuit. The cathode is typically an electronically conducting host into which positive ions are inserted reversibly from the electrolyte as a guest species and are charge-compensated by electrons from the external circuit. A secondary battery, or cell, uses a reaction that can be reversed when current is applied to the battery, thus “recharging” the battery. The chemical reactions at the anode and cathode of a secondary battery must be reversible. On charge, the removal of electrons from the cathode by an external field releases positive ions back to the electrolyte to restore the parent host structure, and the addition of electrons to the anode by the external field attracts charge-compensating positive ions back into the anode to restore it to its original composition.
Traditional electrode materials such as cathode active materials suffer a number of drawbacks. For instance, many traditional cathodes possess an elevated impedance or internal ion resistance that negatively effects battery discharge, and thus, restricts battery performance. As many traditional batteries progress through charge cycles, the deleterious effect of impedance causes an increased hindrance on battery performance.
Thus, there is a need for electrode materials that have improved properties and can improve battery performance.